Proxies are often used at Transport layer and above as a performance enhancement mechanism, especially across WAN links. These proxies rely on peer-to-peer relationships in order to perform their function. This results in a proxy peer network overlaying the layer 3 network and having its own peer-routing information base. In order for the proxies to operate transparently without requiring elaborate configuration, the proxies should be able to derive their routing information from the underlying layer 3 (L3) network.
An approach to the problem is to use manual configuration, but that solution is definitely not attractive to an end user. Another approach is to try to derive the routing information from the L3 routing table of the attached router. The L3 routing table, however, does not have a view beyond the next hop and thus cannot automatically derive this information.